Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, so the safety profile is covered. Beyond that, the description adds genuine context: result ordering ('newest first') and the return fields ('direction, status, duration and timestamps'), plus the underlying REST mapping. It omits paging behavior and any rate-limit or permission notes.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tightly written sentences with the core operation front-loaded and the return summary trailing. The final REST endpoint note is low-value filler, but nothing else is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 7-parameter read-only list tool with no output schema, the description covers what the tool does, how results are ordered, and what fields come back, which is close to sufficient. Pagination semantics (pageToken/nextPageToken) are left to the schema, which is acceptable but leaves a small gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every one of the 7 parameters (including required phoneNumberId/participants and pageToken/maxResults) is already fully documented in the schema with formats and examples. The description only restates the user and date-range filters at a high level, adding no syntax beyond what the schema supplies. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb and resource with scope ('List calls between one of your OpenPhone numbers and a participant'), plus ordering ('newest first') and filter dimensions. It clearly separates itself from the singular get_call sibling by being a list operation, though it never names that sibling explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the filtering language ('optionally filtered by user and created date range'), which suggests when the filters are relevant. There is no explicit when-to-use statement, no exclusion conditions, and no pointer to alternative list tools such as openphone_list_conversations or openphone_list_messages.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.